Method for forming semiconductor device structure

ABSTRACT

A method for forming a semiconductor device structure is provided. The method includes performing a first plasma etching process on a substrate to form a first trench in the substrate. The method includes removing a second portion of the substrate under the bottom surface to form a second trench under and connected to the first trench. The second trench surrounds a third portion of the substrate under the first portion. The third portion has a first sidewall. The first sidewall is inclined relative to the top surface at a second angle, and the first angle is greater than the second angle. The method includes forming an isolation structure in the first trench and the second trench. The method includes forming a gate insulating layer over the top surface and the first inclined surface. The method includes forming a gate over the gate insulating layer and the isolation structure.

CROSS REFERENCE

This application is a Divisional of U.S. application Ser. No. 14/924,326, filed on Oct. 27, 2015, the entirety of which is incorporated by reference herein.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs. Each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs.

In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometric size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling-down process generally provides benefits by increasing production efficiency and lowering associated costs.

However, since feature sizes continue to decrease, fabrication processes continue to become more difficult to perform. Therefore, it is a challenge to form reliable semiconductor devices at smaller and smaller sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It should be noted that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1M are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIG. 2A is a top view of the semiconductor device structure of FIG. 1E, in accordance with some embodiments.

FIG. 2B is a top view of the semiconductor device structure of FIG. 1F, in accordance with some embodiments.

FIG. 2C is a top view of the semiconductor device structure of FIG. 1M, in accordance with some embodiments.

FIG. 3 is a perspective view illustrating the substrate of FIG. 1F, in accordance with some embodiments.

FIGS. 4A-4D are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIG. 5 is a top view of the semiconductor device structure of FIG. 4D, in accordance with some embodiments.

FIG. 6 is a cross-sectional view illustrating the semiconductor device structure along a sectional line I-I′ in FIG. 5, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the subject matter provided. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. It should be understood that additional operations can be provided before, during, and after the method, and some of the operations described can be replaced or eliminated for other embodiments of the method.

FIGS. 1A-1M are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. As shown in FIG. 1A, a substrate 110 is provided, in accordance with some embodiments. The substrate 110 includes, for example, a semiconductor substrate. The semiconductor substrate includes, for example, a semiconductor wafer (such as a silicon wafer) or a portion of a semiconductor wafer.

In some embodiments, the substrate 110 is made of an elementary semiconductor material including silicon or germanium in a single crystal, polycrystal, or amorphous structure. In some other embodiments, the substrate 110 is made of a compound semiconductor, such as silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, an alloy semiconductor, such as SiGe, or GaAsP, or a combination thereof. The substrate 110 may also include multi-layer semiconductors, semiconductor on insulator (SOI) (such as silicon on insulator or germanium on insulator), or a combination thereof.

As shown in FIG. 1A, a mask layer 120 is deposited over an top surface 112 of the substrate 110, in accordance with some embodiments. The mask layer 120 includes oxide (such as silicon oxide), in accordance with some embodiments. The mask layer 120 is deposited using a chemical vapor deposition process or a physical vapor deposition process, in accordance with some embodiments.

As shown in FIG. 1A, a mask layer 130 is deposited over the mask layer 120, in accordance with some embodiments. The mask layers 120 and 130 are made of different materials, in accordance with some embodiments. The mask layer 130 is thicker than the mask layer 120, in accordance with some embodiments. The mask layer 130 includes nitride (such as silicon nitride), in accordance with some embodiments. The mask layer 130 is deposited using a chemical vapor deposition process or a physical vapor deposition process, in accordance with some embodiments.

As shown in FIG. 1A, an anti-reflective layer 140 is formed over the mask layer 130, in accordance with some embodiments. The anti-reflective layer 140 includes a silicon oxide nitride (SiON) material or another suitable material. The anti-reflective layer 140 is formed using a chemical vapor deposition process or a physical vapor deposition process, in accordance with some embodiments.

As shown in FIG. 1B, a photoresist layer 150 is formed over the anti-reflective layer 140, in accordance with some embodiments. The photoresist layer 150 has openings 152, in accordance with some embodiments. The openings 152 expose a portion of the anti-reflective layer 140, in accordance with some embodiments. The photoresist layer 150 is formed using a spin coating process and a photolithography process, in accordance with some embodiments.

As shown in FIG. 1C, the anti-reflective layer 140 and the mask layers 130 and 120 under the openings 152 are removed through the openings 152, in accordance with some embodiments. The removal process includes a dry etching process, in accordance with some embodiments.

After the removal process, the anti-reflective layer 140 has openings 142 under the openings 152, the mask layer 130 has openings 132 under the openings 152, and the mask layer 120 has openings 122 under the openings 152, in accordance with some embodiments. The openings 152, 142, 132, and 122 expose a portion of the substrate 110, in accordance with some embodiments. As shown in FIG. 1D, the photoresist layer 150 is removed, in accordance with some embodiments.

FIG. 2A is a top view of the semiconductor device structure 100 of FIG. 1E, in accordance with some embodiments. FIG. 1E is a cross-sectional view illustrating the semiconductor device structure 100 along a sectional line I-I′ in FIG. 2A, in accordance with some embodiments.

As shown in FIGS. 1E and 2A, a taper etching process is performed to remove a portion of the substrate 110 exposed by the openings 122, 132, and 142 through the openings 122, 132, and 142, in accordance with some embodiments. After the taper etching process, a trench 114 is formed in the substrate 110, in accordance with some embodiments.

The taper etching process includes a plasma etching process, in accordance with some embodiments. The plasma etching process uses an etching gas and a polymer gas, in accordance with some embodiments. The polymer gas is configured to provide a polymer deposition during the taper etching process, in accordance with some embodiments. The etching gas includes CF₄, C₄F₆, or another suitable etching gas. The polymer gas includes CH₂F₂, CH₃F, CHF₃, or another suitable polymer gas.

The trench 114 surrounds portions 116, 117, and 118 of the substrate 110, in accordance with some embodiments. The portion 116 has a top surface 116 a and inclined surfaces 116 b, in accordance with some embodiments. The inclined surfaces 116 b are inclined relative to the top surface 116 a at a first angle θ1, in accordance with some embodiments. The first angle θ1 ranges from about 110° to about 160°, in accordance with some embodiments. The inclined surfaces 116 b connect the top surface 116 a to the bottom surface 114 a of the trench 114, in accordance with some embodiments.

The portion 117 has a top surface 117 a and inclined surfaces 117 b, in accordance with some embodiments. The inclined surfaces 117 b are inclined relative to the top surface 117 a at the first angle θ1, in accordance with some embodiments. The first angle θ1 ranges from about 110° to about 160°, in accordance with some embodiments. The inclined surfaces 117 b connect the top surface 117 a to the bottom surface 114 a of the trench 114, in accordance with some embodiments.

The portion 118 has a top surface 118 a and inclined surfaces 118 b, in accordance with some embodiments. The inclined surfaces 118 b are inclined relative to the top surface 118 a at the first angle θ1, in accordance with some embodiments. The first angle θ1 ranges from about 110° to about 160°, in accordance with some embodiments. The inclined surfaces 118 b connect the top surface 118 a to the bottom surface 114 a of the trench 114, in accordance with some embodiments.

FIG. 2B is a top view of the semiconductor device structure 100 of FIG. 1F, in accordance with some embodiments. FIG. 1F is a cross-sectional view illustrating the semiconductor device structure 100 along a sectional line I-I′ in FIG. 2B, in accordance with some embodiments. FIG. 3 is a perspective view illustrating the substrate 110 of FIG. 1F, in accordance with some embodiments.

As shown in FIGS. 1F, 2B, and 3, a portion of the substrate 110 under the bottom surface 114 a is removed through the openings 122, 132, and 142 and the trench 114, in accordance with some embodiments. After the removal process, a trench 119 is formed in the substrate 110, in accordance with some embodiments. The trench 119 is under the trench 114, in accordance with some embodiments.

The trench 119 is connected to the trench 114, in accordance with some embodiments. The trenches 114 and 119 together form a trench T, in accordance with some embodiments. The trench 119 surrounds portions 216, 217, and 218 of the substrate 110, in accordance with some embodiments.

The portions 216, 217, and 218 are under the portions 116, 117, and 118 respectively, in accordance with some embodiments. The portions 116 and 216 are together form an active island A1, in accordance with some embodiments. The portions 117 and 217 are together form an active island A2, in accordance with some embodiments. The portions 118 and 218 are together form an active island A3, in accordance with some embodiments.

As shown in FIGS. 1F, 2B, and 3, the portion 216 has sidewalls 216 a, in accordance with some embodiments. The sidewalls 216 a are inclined relative to the top surface 116 a at a second angle θ2, in accordance with some embodiments. The first angle θ1 is greater than the second angle θ2, in accordance with some embodiments.

The second angle θ2 ranges from about 90° to about 100°, in accordance with some embodiments. The inclined surface 116 b is inclined relative to the sidewall 216 a at a third angle θ3, in accordance with some embodiments. The third angle θ3 ranges from about 110° to about 170°, in accordance with some embodiments.

The inclined surface 116 b connects the top surface 116 a to the sidewall 216 a thereunder, in accordance with some embodiments. The inclined surface 116 b directly connects the top surface 116 a to the sidewall 216 a thereunder, in accordance with some embodiments. There are no other surfaces between the inclined surface 116 b and the top surface 116 a, in accordance with some embodiments. There are no other surfaces between the inclined surface 116 b and the sidewall 216 a thereunder, in accordance with some embodiments.

As shown in FIGS. 1F, 2B, and 3, a ridge line R1 is between the top surface 116 a and the inclined surface 116 b, in accordance with some embodiments. In some embodiments, a ridge line R2 is between the inclined surface 116 b and the sidewall 216 a. The ridge lines R1 and R2 are spaced apart from each other, in accordance with some embodiments.

As shown in FIGS. 1F, 2B, and 3, the portion 217 has sidewalls 217 a, in accordance with some embodiments. The sidewalls 217 a are inclined relative to the top surface 117 a at a second angle θ2, in accordance with some embodiments. The first angle θ1 is greater than the second angle θ2, in accordance with some embodiments.

The second angle θ2 ranges from about 90° to about 100°, in accordance with some embodiments. The inclined surface 117 b is inclined relative to the sidewall 217 a at a third angle θ3, in accordance with some embodiments. The third angle θ3 ranges from about 110° to about 170°, in accordance with some embodiments.

If the first angle θ1 is less than 110°, the stress at the top corners TC1, TC2, and TC3 of the active islands A1, A2, and A3 may be too great to form a gate insulating layer thereon. If the first angle θ1 is greater than 160° (i.e. the third angle θ3 is less than 120°), the stress at the top corners TC1, TC2, and TC3 of the active islands A1, A2, and A3 may be too great to form a gate insulating layer thereon.

As shown in FIGS. 1F, 2B, and 3, a ridge line R3 is between the top surface 117 a and the inclined surface 117 b, in accordance with some embodiments. In some embodiments, a ridge line R4 is between the inclined surface 117 b and the sidewall 217 a. The ridge lines R3 and R4 are spaced apart from each other, in accordance with some embodiments.

As shown in FIGS. 1F, 2B, and 3, the portion 218 has sidewalls 218 a, in accordance with some embodiments. The sidewalls 218 a are inclined relative to the top surface 118 a at a second angle θ2, in accordance with some embodiments. The first angle θ1 is greater than the second angle θ2, in accordance with some embodiments.

The second angle θ2 ranges from about 90° to about 100°, in accordance with some embodiments. The inclined surface 118 b is inclined relative to the sidewall 218 a at a third angle θ3, in accordance with some embodiments. The third angle θ3 ranges from about 110° to about 170°, in accordance with some embodiments.

As shown in FIGS. 1F, 2B, and 3, a ridge line R5 is between the top surface 118 a and the inclined surface 118 b, in accordance with some embodiments. In some embodiments, a ridge line R6 is between the inclined surface 118 b and the sidewall 218 a. The ridge lines R5 and R6 are spaced apart from each other, in accordance with some embodiments. In some embodiments, the top surfaces 116 a, 117 a, and 118 a, the sidewall 216 a, 217 a, and 218 a, and the inclined surface 116 b, 117 b, and 118 b are substantially planar surfaces.

The removal process includes a plasma etching process, in accordance with some embodiments. The plasma etching process uses an etching gas, in accordance with some embodiments. The plasma etching process further uses a polymer gas, in accordance with some embodiments. The polymer gas is configured to provide a polymer deposition during the plasma etching process, in accordance with some embodiments. The etching gas includes CF₄, C₄F₆, or another suitable etching gas. The polymer gas includes CH₂F₂, CH₃F, CHF₃, or another suitable polymer gas.

In some embodiments, the polymer gas used in the taper etching process has a first concentration which is greater than a second concentration of the polymer gas used in the removal process for forming the trench 119. Therefore, relative to the bottom surface 111 or the top surfaces 116 a, 117 a, and 118 a, the inclined surfaces 116 b are more inclined than the sidewalls 216 a, the inclined surfaces 117 b are more inclined than the sidewalls 217 a, and the inclined surfaces 118 b are more inclined than the sidewalls 218 a.

As shown in FIG. 1G, an insulating layer 160 a is deposited over the substrate 110 to fill the trenches 114 and 119, in accordance with some embodiments. The insulating layer 160 a fills the openings 122, 132, and 142 and covers the anti-reflective layer 140, the mask layers 120 and 130, and the substrate 110, in accordance with some embodiments. The insulating layer 160 a includes oxide (such as silicon oxide), in accordance with some embodiments. The insulating layer 160 a may be formed by a chemical vapor deposition (CVD) process.

As shown in FIG. 1H, the anti-reflective layer 140 and the insulating layer 160 a over the anti-reflective layer 140 are removed, in accordance with some embodiments. The removal process includes a chemical mechanical polishing (CMP) process, in accordance with some embodiments. As shown in FIG. 1I, the mask layer 130 is removed, in accordance with some embodiments. The removal process includes a wet etching process, in accordance with some embodiments.

The trench T adjacent to the inclined surface 116 b, 117 b, or 118 b (i.e. the trench 114) has a first depth D1, in accordance with some embodiments. The trench T adjacent to the sidewall 216 a, 217 a, or 218 a (i.e. the trench 119) has a second depth D2, in accordance with some embodiments. The second depth D2 is greater than the first depth D1, in accordance with some embodiments.

The inclined surface 116 b has a length L1, in accordance with some embodiments. The sidewall 216 a has a length L2, in accordance with some embodiments. The length L2 is greater than the length L1, in accordance with some embodiments.

The inclined surface 117 b has a length L3, in accordance with some embodiments. The sidewall 217 a has a length L4, in accordance with some embodiments. The length L4 is greater than the length L3, in accordance with some embodiments.

The inclined surface 118 b has a length L5, in accordance with some embodiments. The sidewall 218 a has a length L6, in accordance with some embodiments. The length L6 is greater than the length L5, in accordance with some embodiments.

As shown in FIG. 1J, the mask layer 120 is removed, in accordance with some embodiments. The removal process includes a dry etching process and/or a wet etching process, in accordance with some embodiments. In some embodiments, the removal process also removes an upper portion of the insulating layer 160 a to form an isolation structure 160.

The isolation structure 160 does not cover the inclined surfaces 116 b, 117 b, and 118 b, in accordance with some embodiments. The isolation structure 160 exposes the entire inclined surfaces 116 b, 117 b, and 118 b, in accordance with some embodiments. The isolation structure 160 covers the sidewalls 216 a, 217 a, and 218 a, in accordance with some embodiments.

As shown in FIG. 1K, gate insulating layers 172, 174, and 176 are formed over the active islands A1, A2, and A3 respectively, in accordance with some embodiments. The gate insulating layers 172, 174, and 176 includes oxide (such as silicon oxide), in accordance with some embodiments.

The gate insulating layers 172, 174, and 176 are formed using a thermal oxidation process, in accordance with some embodiments. The gate insulating layers 172, 174, and 176 includes an oxide of a material of the active islands A1, A2, and A3 respectively, in accordance with some embodiments.

The embodiments perform the taper etching process to form the inclined surface 116 b between the top surface 116 a and the sidewall 216 a, and the first angle θ1 between the top surface 116 a and the inclined surface 116 b is greater than the second angle θ2 between the top surface 1 16a and the sidewall 216 a (as shown in FIG. 1F). Therefore, the formation of the inclined surface 116 b may reduce the stress at the top corner TC1 of the active island A1. The stress at the top corner TC1 of the active island A1 is resulted from the small angle θ2 between the top surface 116 a and the sidewall 216 a.

Since the stress is reduced, the formation of the gate insulating layer 172 over the top corner TC1 of the active island A1 is improved. Similarly, the formation of the gate insulating layers 174 and 176 over the top corners TC2 and TC3 of the active island A2 and A3 is improved as well.

The gate insulating layer 172 covers the top surface 116 a, the ridge line R1, and the inclined surface 116 b, in accordance with some embodiments. The gate insulating layer 172 continuously covers the top surface 116 a, the ridge line R1, and the inclined surface 116 b, in accordance with some embodiments. The gate insulating layer 172 is a continuous layer, in accordance with some embodiments.

The gate insulating layer 172 includes portions 172 a and 172 b, in accordance with some embodiments. The portion 172 a is over the top surface 116 a, and the portion 172 b is over the inclined surface 116 b, in accordance with some embodiments. The portion 172 b has a thickness T1, and the portion 172 a has a thickness T2, in accordance with some embodiments. The thickness T1 is equal to or greater than the thickness T2, in accordance with some embodiments.

The inclined surface 116 b includes a (110) crystal orientation, in accordance with some embodiments. The top surface 116 a includes a (100) crystal orientation, in accordance with some embodiments. The oxidation rate of the (110) crystal orientation is greater than the oxidation rate of the (100) crystal orientation, in accordance with some embodiments. Therefore, the thickness T1 is equal to or greater than the thickness T2, in accordance with some embodiments.

The gate insulating layer 174 covers the top surface 117 a, the ridge line R3, and the inclined surface 117 b, in accordance with some embodiments. The gate insulating layer 174 continuously covers the top surface 117 a, the ridge line R3, and the inclined surface 117 b, in accordance with some embodiments. The gate insulating layer 174 is a continuous layer, in accordance with some embodiments.

The gate insulating layer 174 includes portions 174 a and 174 b, in accordance with some embodiments. The portion 174 a is over the top surface 117 a, and the portion 174 b is over the inclined surface 117 b, in accordance with some embodiments. The portion 174 b has a thickness T3, and the portion 174 a has a thickness T4, in accordance with some embodiments. The thickness T3 is equal to or greater than the thickness T4, in accordance with some embodiments.

The inclined surface 117 b includes a (110) crystal orientation, in accordance with some embodiments. The top surface 117 a includes a (100) crystal orientation, in accordance with some embodiments. The oxidation rate of the (110) crystal orientation is greater than the oxidation rate of the (100) crystal orientation, in accordance with some embodiments. Therefore, the thickness T3 is equal to or greater than the thickness T4, in accordance with some embodiments.

The gate insulating layer 176 covers the top surface 118 a, the ridge line R5, and the inclined surface 118 b, in accordance with some embodiments. The gate insulating layer 176 continuously covers the top surface 118 a, the ridge line R5, and the inclined surface 118 b, in accordance with some embodiments. The gate insulating layer 176 is a continuous layer, in accordance with some embodiments.

The gate insulating layer 176 includes portions 176 a and 176 b, in accordance with some embodiments. The portion 176 a is over the top surface 118 a, and the portion 176 b is over the inclined surface 118 b, in accordance with some embodiments. The portion 176 b has a thickness T5, and the portion 176 a has a thickness T6, in accordance with some embodiments. The thickness T5 is equal to or greater than the thickness T6, in accordance with some embodiments.

The inclined surface 118 b includes a (110) crystal orientation, in accordance with some embodiments. The top surface 118 a includes a (100) crystal orientation, in accordance with some embodiments. The oxidation rate of the (110) crystal orientation is greater than the oxidation rate of the (100) crystal orientation, in accordance with some embodiments. Therefore, the thickness T5 is equal to or greater than the thickness T6, in accordance with some embodiments.

As shown in FIG. 1L, a gate material layer 180 a is deposited over the gate insulating layers 172, 174, and 176, in accordance with some embodiments. The gate material layer 180 a is deposited using a chemical vapor deposition process or a physical vapor deposition process, in accordance with some embodiments. The gate material layer 180 a includes a polysilicon material or another suitable conductive material.

FIG. 2C is a top view of the semiconductor device structure 100 of FIG. 1M, in accordance with some embodiments. FIG. 1M is a cross-sectional view illustrating the semiconductor device structure 100 along a sectional line I-I′ in FIG. 2C, in accordance with some embodiments. FIG. 4A is a cross-sectional view illustrating the semiconductor device structure 100 along a sectional line II-II′ in FIG. 2C, in accordance with some embodiments.

As shown in FIGS. 1M, 2C, and 4A, portions of the gate insulating layers 172, 174, and 176 and the gate material layer 180 a are removed, in accordance with some embodiments. The remaining gate material layer 180 a forms a gate 180 over the gate insulating layer 172, in accordance with some embodiments. The gate 180 and the gate insulating layer 172 together form a gate stack G, in accordance with some embodiments. The removal process includes a photolithography process and an etching process, in accordance with some embodiments.

The gate 180 is over the gate insulating layer 172 and the isolation structure 160, in accordance with some embodiments. The gate 180 crosses the active island A1, in accordance with some embodiments. The gate insulating layer 172 is in direct contact with the active island A1, the isolation structure 160, and the gate 180, in accordance with some embodiments. The gate insulating layer 172 separates the gate 180 from the active island A1, in accordance with some embodiments.

Since the formation of the gate insulating layer 172 over the active island A1, especially over the top corner TC1, is improved by the formation of the inclined surface 116 b, the gate insulating layer 172 is able to electrically insulate the gate 180 from the active island A1. Since the thickness T1 of the gate insulating layer 172 over the inclined surface 116 b is equal to or greater than the thickness T2 of the gate insulating layer 172 over the top surface 116 a (as shown in FIG. 1K), the reliability of the gate insulating layer 172 is improved, in accordance with some embodiments.

FIGS. 4A-4D are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. After the step of FIG. 4A, as shown in FIG. 4B, a spacer layer 190 is deposited over the substrate 110 to cover the gate stack G, in accordance with some embodiments. The spacer layer 190 is deposited using a CVD process, in accordance with some embodiments. The spacer layer 190 includes insulating materials, such as silicon oxide or silicon nitride, in accordance with some embodiments.

As shown in FIG. 4C, a portion of the spacer layer 190 is removed, in accordance with some embodiments. The spacer layer 190 remains over the sidewalls S of the gate stack G, in accordance with some embodiments. The spacer layer 190 is configured to electrically isolate the gate 180 from other devices and to act as a mask layer in a subsequent ion implantation process, in accordance with some embodiments. The removal process includes an anisotropic etching process (such as a dry etching process), in accordance with some embodiments.

FIG. 5 is a top view of the semiconductor device structure 100 of FIG. 4D, in accordance with some embodiments. FIG. 4D is a cross-sectional view illustrating the semiconductor device structure 100 along a sectional line II-II′ in FIG. 5, in accordance with some embodiments. FIG. 6 is a cross-sectional view illustrating the semiconductor device structure 100 along a sectional line I-I′ in FIG. 5, in accordance with some embodiments.

As shown in FIG. 4D, 5, and 6, doped regions 111 are formed in the semiconductor substrate 110, in accordance with some embodiments. The formation of the doped regions 111 includes as an ion implantation process, in accordance with some embodiments. The ion implantation process is performed to introduce p-type impurities (e.g., boron) or n-type impurities (e.g., phosphorus) into the semiconductor substrate 110, in accordance with some embodiments.

The doped regions 111 are a doped source region and a doped drain region, in accordance with some embodiments. The gate stack G is located between the doped regions 111, in accordance with some embodiments. The gate stack G, the spacer layer 190, and the doped regions 111 constitute a transistor device S, in accordance with some embodiments.

Since the formation of the inclined surface 116 b helps the formation of the gate insulating layer 172 over the active island A1 to electrically insulate the gate 180 from the active island A1, the yield of the transistor device S is improved, in accordance with some embodiments. In some other embodiments, the gate 180 of the transistor device S is replaced by a metal gate.

In accordance with some embodiments, semiconductor device structures and methods for forming the same are provided. The methods (for forming the semiconductor device structure) form an inclined surface of a top corner of an active island to help the formation of a gate insulating layer over the active island, especially over the top corner. Therefore, the reliability of the gate insulating layer is improved, and the yield of the transistor device including the gate insulating layer is improved as well.

In accordance with some embodiments, a method for forming a semiconductor device structure is provided. The method includes performing a first plasma etching process on a substrate to form a first trench in the substrate. The first plasma etching process uses a first etching gas and a first deposition gas. The first trench surrounds a first portion of the substrate. The first portion has a top surface and a first inclined surface. The first inclined surface connects the top surface to a bottom surface of the first trench, and the first inclined surface is inclined relative to the top surface at a first angle. The method includes removing a second portion of the substrate under the bottom surface to form a second trench under and connected to the first trench. The second trench surrounds a third portion of the substrate under the first portion. The third portion has a first sidewall. The first sidewall is inclined relative to the top surface at a second angle, and the first angle is greater than the second angle. The method includes forming an isolation structure in the first trench and the second trench. The method includes forming a gate insulating layer over the top surface and the first inclined surface. The method includes forming a gate over the gate insulating layer and the isolation structure. The gate crosses the first portion.

In accordance with some embodiments, a method for forming a semiconductor device structure is provided. The method includes performing a first plasma etching process on a substrate to form a first trench in the substrate. The first plasma etching process uses a first etching gas and a first deposition gas, and the first trench has a bottom surface. The method includes performing a second plasma etching process on the bottom surface to form a second trench. The second plasma etching process uses a second etching gas and a second deposition gas. A first concentration of the first deposition gas is greater than a second concentration of the second deposition gas. The method includes forming an isolation structure in the first trench and the second trench. The method includes forming a gate insulating layer over the substrate. The method includes forming a gate over the gate insulating layer.

In accordance with some embodiments, a method for forming a semiconductor device structure is provided. The method includes performing a first plasma etching process on a substrate to form a first trench in the substrate. The first plasma etching process uses a first etching gas and a first deposition gas. The first trench surrounds a first portion of the substrate. The first portion has a top surface and a first inclined surface. The first inclined surface connects the top surface to a bottom surface of the first trench, and the first inclined surface is inclined relative to the top surface at a first angle. The method includes removing a second portion of the substrate under the bottom surface to form a second trench under and connected to the first trench. The second trench surrounds a third portion of the substrate under the first portion. The third portion has a first sidewall. The first sidewall is inclined relative to the top surface at a second angle, and the first angle is greater than the second angle. The method includes forming an isolation structure in the first trench and the second trench. The method includes after the formation of the isolation structure, performing an oxidation process on the substrate to form a continuous gate insulating layer on the top surface and the first inclined surface. The method includes forming a gate over the gate insulating layer and the isolation structure. The gate crosses the first portion.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming a semiconductor device structure, comprising: performing a first plasma etching process on a substrate to form a first trench in the substrate, wherein the first plasma etching process uses a first etching gas and a first deposition gas, the first trench surrounds a first portion of the substrate, the first portion has a top surface and a first inclined surface, the first inclined surface connects the top surface to a bottom surface of the first trench, and the first inclined surface is inclined relative to the top surface at a first angle; removing a second portion of the substrate under the bottom surface to form a second trench under and connected to the first trench, wherein the second trench surrounds a third portion of the substrate under the first portion, the third portion has a first sidewall, the first sidewall is inclined relative to the top surface at a second angle, and the first angle is greater than the second angle; forming an isolation structure in the first trench and the second trench; forming a gate insulating layer over the top surface and the first inclined surface; and forming a gate over the gate insulating layer and the isolation structure, wherein the gate crosses the first portion.
 2. The method for forming a semiconductor device structure as claimed in claim 1, wherein the first deposition gas comprises CH₂F₂, CH₃F, or CHF₃.
 3. The method for forming a semiconductor device structure as claimed in claim 1, wherein the formation of the first trench comprises: forming a mask layer over the substrate, wherein the mask layer has an opening exposing a fourth portion of the substrate; and performing the first plasma etching process to remove the fourth portion of the substrate through the opening so as to form the first trench.
 4. The method for forming a semiconductor device structure as claimed in claim 3, wherein the formation of the second trench comprises: performing a second plasma etching process to remove the second portion of the substrate through the opening and the first trench so as to form the second trench.
 5. The method for forming a semiconductor device structure as claimed in claim 4, wherein the second plasma etching process uses a second etching gas and a second deposition gas.
 6. The method for forming a semiconductor device structure as claimed in claim 5, wherein the second deposition gas comprises CH₂F₂, CH₃F, or CHF₃.
 7. The method for forming a semiconductor device structure as claimed in claim 5, wherein the formation of the isolation structure comprises: forming an insulating layer over the mask layer and in the opening, the first trench, and the second trench; removing the insulating layer outside of the opening, the first trench, and the second trench; and removing the mask layer.
 8. The method for forming a semiconductor device structure as claimed in claim 1, wherein the isolation structure has a second inclined surface, the first inclined surface and the second inclined surface form second sidewalls of a recess, and the gate extends into the recess.
 9. The method for forming a semiconductor device structure as claimed in claim 8, wherein the gate insulating layer extends into the recess and partially covers the second inclined surface, the recess is filled with the gate and the gate insulating layer, and the gate is over the isolation structure partially.
 10. A method for forming a semiconductor device structure, comprising: performing a first plasma etching process on a substrate to form a first trench in the substrate, wherein the first plasma etching process uses a first etching gas and a first deposition gas, and the first trench has a bottom surface; performing a second plasma etching process on the bottom surface to form a second trench, wherein the second plasma etching process uses a second etching gas and a second deposition gas, a first concentration of the first deposition gas is greater than a second concentration of the second deposition gas; forming an isolation structure in the first trench and the second trench; forming a gate insulating layer over the substrate; and forming a gate over the gate insulating layer.
 11. The method for forming a semiconductor device structure as claimed in claim 10, wherein the first deposition gas comprises CH₂F₂, CH₃F, or CHF₃.
 12. The method for forming a semiconductor device structure as claimed in claim 11, wherein the first deposition gas and the second deposition gas comprise a same deposition gas.
 13. The method for forming a semiconductor device structure as claimed in claim 10, wherein the formation of the first trench and the second trench comprises: forming a mask layer over the substrate, wherein the mask layer has an opening exposing a third portion of the substrate; performing the first plasma etching process to remove the third portion of the substrate through the opening so as to form the first trench; and performing the second plasma etching process to remove a fourth portion of the substrate under the bottom surface through the opening and the first trench so as to form the second trench.
 14. The method for forming a semiconductor device structure as claimed in claim 10, wherein the first trench has a first sidewall with a first slope, the second trench has a second sidewall with a second slope, and the first slope is less than second slope.
 15. The method for forming a semiconductor device structure as claimed in claim 14, wherein the isolation structure has an inclined surface, the first sidewall and the inclined surface form third sidewalls of a recess, and the gate extends into the recess, the gate insulating layer extends into the recess and partially covers the inclined surface, the recess is filled with the gate and the gate insulating layer, and the gate is over the isolation structure partially.
 16. A method for forming a semiconductor device structure, comprising: performing a first plasma etching process on a substrate to form a first trench in the substrate, wherein the first plasma etching process uses a first etching gas and a first deposition gas, the first trench surrounds a first portion of the substrate, the first portion has a top surface and a first inclined surface, the first inclined surface connects the top surface to a bottom surface of the first trench, and the first inclined surface is inclined relative to the top surface at a first angle; removing a second portion of the substrate under the bottom surface to form a second trench under and connected to the first trench, wherein the second trench surrounds a third portion of the substrate under the first portion, the third portion has a first sidewall, the first sidewall is inclined relative to the top surface at a second angle, and the first angle is greater than the second angle; forming an isolation structure in the first trench and the second trench; after the formation of the isolation structure, performing an oxidation process on the substrate to form a continuous gate insulating layer on the top surface and the first inclined surface; and forming a gate over the gate insulating layer and the isolation structure, wherein the gate crosses the first portion.
 17. The method for forming a semiconductor device structure as claimed in claim 16, wherein during the oxidation process, a first oxidation rate of the substrate constituting the first inclined surface is greater than a second oxidation rate of the substrate constituting the top surface.
 18. The method for forming a semiconductor device structure as claimed in claim 17, wherein the inclined surface comprises a (110) crystal orientation, the top surface comprises a (100) crystal orientation, the gate insulating layer has a fourth portion and a fifth portion, the fourth portion is over the first inclined surface, the fifth portion is over the top surface, and a first thickness of the fourth portion is greater than a second thickness of the fifth portion.
 19. The method for forming a semiconductor device structure as claimed in claim 16, wherein the isolation structure has a second inclined surface, the first inclined surface and the second inclined surface form second sidewalls of a recess, and the gate extends into the recess.
 20. The method for forming a semiconductor device structure as claimed in claim 19, wherein the gate insulating layer extends into the recess and partially covers the second inclined surface, the recess is filled with the gate and the gate insulating layer, and the gate is over the isolation structure partially. 